单项选择题

A．4.2 billion years ago.
B．3.3 billion years ago.
C．2.9 billion years ago.
D．1.2 billion years ago.
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单项选择题
A．He worked for a medical periodical.B．He published a paper about computer science.C．He suggested a link between smoke and lung cancer.D．He opened a hospital with his partner.
A．He worked for a medical periodical.
B．He published a paper about computer science.
C．He suggested a link between smoke and lung cancer.
D．He opened a hospital with his partner.
填空题
magazines
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